1. Field of the Invention
The invention relates to the flow of gas through lines. More particularly, it relates to such flow through large lines having high flow rate requirements.
2. Description of the Prior Art
There are a variety of industrial operations that require the pumping of gases through relatively large size lines. As the diameter of the line increases, the flow rate requirements of the gas are correspondingly increased. For various applications, the providing of such high flow rate capacity can pose a practical problem from an operational viewpoint. In some instances flow rate limitations may preclude the carrying out of a desired operation with conditions requiring relatively high flow rates.
The in-situ cleaning of water or gas pipelines is a highly desirable industrial operation in which gas pumper flow rate limitations have tended to preclude application to large size lines. In such in-situ cleaning, an industrial service activity provided by Union Carbide Industrial Services Company (UCISCO) as the Sandjet.RTM. process, a high velocity, propelling gas stream (e.g. nitrogen) having cleaning particle entrained therein is injected into the line to be cleaned. The turbulent and swirling motion of the propelling gas stream in the line induces a high radial velocity to the cleaning particles, with sufficient energy to dislodge deposits from the inner walls of the line. Such dislodged deposits are removed from the line with the propelling gas stream and cleaning particles. The in-situ cleaning operation is continued, through a number of relatively short cleaning runs, until the unwanted deposit has been removed, as evidenced by the removal of a clean, essentially deposit-free gas stream from the outlet end of the line. A sufficient supply of propelling gas must be available for this in-situ cleaning process, which is commonly carried out at exit flow velocities of about 14,000 to 20,000 feet per minute, with 16,000 feet per minute being a typical exit flow velocity for such applications.
The in-situ cleaning process is normally limited to the cleaning of lines having a maximum diameter of 12 inches due to increasingly higher flow rate requirements for larger lines. Thus, at said 16,000 feet per minute exit velocity, a 6" line requires a gas flow rate of 3,142 scfm (standard cubic feet per minute), said flow rate increasing to 12,566 scfm for a 12" line, to 28,274 scfm for an 18" line, and to 50,265 scfm for a 24" line.
A conventional pumper for the vaporizing and pumping of liquid nitrogen, as employed in common commercial practice, typically has a maximum flow capacity of about 3,800 scfm. Thus, a 6" line can be cleaned using one such pumper, while four pumpers are required for a 12" line. Eight pumpers would be required for an 18" line, and a total of fourteen pumpers would be required for a 24" line. Under such circumstances, the use of such pumpers for the cleaning of lines larger than 12" becomes unduly expensive and presents practical logistical problems because of the large number of pumpers required. For certain cross country pipeline applications, such problems are obviated by the use of a technique referred to as ballasting, wherein a part of a line is pumped to the desired pressure and is then used to supply the required high flow rate needed in the in-situ cleaning of another portion of the line. For plant operations, ballasting has not been found feasible because no suitable line is typically available for ballasting. In order to achieve the required high flow rates of large size lines using pumpers only, a fleet of pumpers would have to be available for a particular job, and all of the pumpers would have to be connected to a common manifold, be supplied with liquid nitrogen and be brought on line simultaneously for each run of the in-situ cleaning process. Such an operation becomes increasingly more difficult and expensive with each additional pumper.
For some in-situ cleaning applications, it may be feasible to use air in place of nitrogen as the propelling gas. With respect to supplying high flow rates, however, it was determined that a 1,000 hp compressor will supply about 1,500 scfm of air. As with the pumpers referred to above, a large number of air compressors would be required for high flow operations, and the cost and space requirements associated with the use of air compressors would be prohibitive.
While in-situ cleaning of high flow rate lines has been precluded for the reasons indicated above, there is nevertheless a desire in the art for the use of the in-situ cleaning process for the cleaning of larger diameter lines. The inherent advantages of the in-situ process are such, compared with the alternatives of cutting open sections of the line, cleaning by mechanical means, and re-assembling the line, that it would readily be used for large size lines if a convenient means for providing the high flow rate requirements could be found.
It is an object of the invention, therefore, to provide a process and apparatus for the supply of gas at high flow rates.
It is another object of the invention to provide a process and apparatus for the supply of gas for in-situ cleaning and other operations requiring high flow rates for relatively short periods of time.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features of which are particularly pointed out in the appended claims.